Email is considered a store-and-forward technology in which a message is stored by a server of a network center and forwarded to a target device when the target device is powered and connected to a network such as the Internet. Email messages are usually not limited in length. Computer and Internet companies developed instant messaging (IM) to provide direct, two-way text and graphics messaging. Instant messaging is generally considered a distinctly Internet product, and also usually does not place any limit on the length of messages. Instant messages are generally not stored and forwarded like conventional email. Instead, instant messages are typically handled through a central server in a protocol that is usually separate from email or web traffic to provide direct communication between clients. Users typically run a resident client application that provides IM services.
Wireless phone companies developed short message service (SMS) to provide a text messaging compliment to voice communication services. SMS was generally designed for the thinner communication channel of the wireless environment. Message length is usually limited (typically 80 or 160 characters), and the receiver must have a compatible mobile phone. Messages are usually handled by a network center, since SMS is a store-and-forward technology. In the case of SMS, a message is temporarily stored by a server of the network center and forwarded to a mobile device when the mobile device is powered and connected to a network such as a cellular network.
Although SMS is considered a store-and-forward technology, SMS messages are delivered to the mobile client whenever the mobile device is powered and connected to the network, rather than when the user launches a client message service like email. Thus, SMS and IM systems allow users to send messages that are generally faster and more intrusive than email or other text messaging systems. Instead of waiting for the receiver to check a message center (mailbox), these messages are delivered whenever the receiver is accessible by a message server.
Instant wireless is a wireless version of instant text messaging in which information is being sent through wireless networks in real-time, rather than being handled through a store-and-forward mechanism. As indicated above, store-and-forward delivery is traditionally used in many email and batched transaction handling systems. Typically, a message is stored in a server and then after a pre-defined delay, it is processed and sent to the destination server where it is picked up by the recipient. Instant wireless may be considered a one-way, real-time, digital telephone message conversation (not voice) with an answering machine, using a wireless network. It is considered communication with an answering machine, because the recipient at his/her option may not respond instantly. Since the communication channel does not necessarily stay open between sender and recipient, instant wireless is generally not considered true two-way communication. However, instant wireless does send messages instantly, rather than wait for a batch to accumulate. A pre-requisite to instant wireless is that the destination device is turned on and connected through wireline or wireless connection. It generally takes less effort to write code for instant messaging than it is for store-and-forward messaging. It is also generally more efficient with regard to processing costs. However, instant wireless generally requires a more costly infrastructure.